We are studying the relation of the accessory optic system of birds to stabilizing eye movements in particular optokinetic nystagmus (OKN). Using the 2-deoxyglocose technique, we have identified areas of the accessory optic system and pretectum that become more metabolically active during vertical optokinetic stimulation. Using single unit recording, we are studying the organization of these areas, and have evidence that the accessory optic system is organized in terms of a vestibular coordinate system. Studies of optokinetic nystagmus to stimulus movement in non-horizontal directions reveal striking assymetries in gain, particularly in directions of stimulus motion that correspond to the ones that would be experienced during head movement that maximally stimulates one of the canals. We plan to study these assymetries in detail and try to relate them to response properties of accessory optic system neurons.